In the course of the last few years, there has been a growing use, in automatic vending machines for preparing and dispensing beverages, of so-called capsules, in particular such capsules of a hermetically sealed type, which contain a raw material ready for brewing. These sealed capsules are constituted by semi-rigid envelopes provided with a collet, which create a physical barrier separating their contents from the surrounding ambient. In beverage vending machines, capsules of this kind are certainly by far preferably over both the traditional pre-filled filters, i.e. filters that are filled in advance with the raw material for brewing, and those capsules that are constituted by a semi-rigid envelope comprising a pair of surfaces acting as filtering elements, i.e. elements that enable the brew to pass therethrough, while retaining the raw material within the same capsule. The main advantage deriving from the afore-mentioned hermetically sealed capsules lies in the fact that the raw material contained in these capsules is effectively and reliably preserved from any contact with the outside ambient, thereby ensuring a maximum extent of hygiene, as well as an optimum preservation of the flavor, fragrance and the other properties of the content thereof over prolonged periods of time. This is basically why this kind of packaging is highly preferable, especially in those vending machines, which prepare and dispense beverages of an aromatic kind, such as for instance coffee, tisanes or other kinds of hot infusions.
Largely known in the art is the fact that the use of sealed capsules in automatic vending machines requires these machines to be provided with brewing units that comprise devices adapted to accommodate and hold the capsules themselves, as well as devices adapted to ensure the water-tightness of the brewing chamber and devices adapted to pierce the capsule in order to enable water to come into contact with the raw material contained therein. When a brewing unit of the just described kind is in operation, some of the members constituting the same unit are set in motion, so as to displace relative to each other, by means of appropriate mechanical devices that are usually operated by an electric motor. The fact that such brewing units are operated solely by mechanical members and devices is disadvantageous in that the operating accuracy of such mechanical members, and as a result the proper production of the beverage, are strongly dependent on the manufacturing and assembly tolerances of the various mechanical parts involved, as well as the increasing wear-down state of the materials which said mechanical parts are made of. To particularly suffer from this drawback is chiefly the mating accuracy of those elements constituting the brewing unit, which are temporarily associated with each other in order to tightly seal the brewing chamber during the beverage preparation process. It can be readily appreciated that, if such a mating accuracy is not perfect, or becomes imperfect after a certain number of working cycles of the brewing unit, there will occur leakage problems involving both liquid and raw material, which eventually affect the quality of the beverage being produced. Another device that is particularly affected by this drawback is one that causes the capsule to be pierced. In prior-art brewing units, the piercing operation is performed with the aid of means that press the capsule against a device comprising one or more projections that are so shaped as to be able to pierce the material which the capsule is made of. Even in this case, it can be readily appreciated that if the pressing action intervening between the capsule and the piercing device cannot be brought about to full intensity, i.e. loses some of its force due to the inaccuracy of the mechanical devices moving or actuating the various parts forming the brewing unit, the resulting beverage will not be produced correctly.
Known from the disclosure in U.S. Pat. No. 6,431,055 is a brewing unit for the preparation of espresso coffee, the component parts of which are actuated by the action of pressurized water from the machine pump without any further electric or pneumatic control being used. The brewing unit described in this patent publication is designed to work with the use of loose coffee powder or filter bags that are pre-filled with raw material, of the type of those provided in the form of a capsule constituted by a semi-rigid envelope with a base and a bottom acting as a filter. Further to the already mentioned poor preservation of the raw material contained in capsules provided with filtering surfaces, the brewing unit described in U.S. Pat. No. 6,431,055 can by no means operate by using the more advantageous capsules of the hermetically sealed type, since no device or member adapted to enable the capsules to be dully pierced is provided therein.